1. Field of the Invention
The present invention relates to a semiconductor device and a process for manufacturing the same. More particularly, the present invention relates to a semiconductor device having an improved interlayer insulating film and a process for manufacturing the same.
2. Background Art
The recent finer patterning of semiconductor devices has posed a serious problem with lead line delay due to the capacitance of the interlayer insulating film. Reducing the capacitance of the interlayer insulating film is an important future subject. This is true particularly in the case of lead lines finer than 0.3 m. Thus, there is a demand for a new interlayer insulating film which has a low dielectric constant and good burying properties and surface leveling properties.
It is expected that this demand will be satisfied by fluorine-containing silicon oxide film (referred to as SiOF film hereinafter). See "High density plasma CVD fluoro-silicate glass gap-filling for sub-half micron CMOS devices" (Proceedings of VMIC Conference 1997).
The SiOF film has a decreased dielectric constant on account of the introduction of Si--F bonds into a silicon oxide film. For example, a silicon oxide film (free of Si--F bonds) decreases in dielectric constant from 4.4 to 3.5 when it contains about 10% fluorine.
The decrease in dielectric constant is probably due to the presence of Si--F bonds in the film in such a way that the Si--O network is partly broken and minute voids (or defects) are formed in the film. Such minute voids are three-membered rings as shown in FIG. 7(a) or four-membered rings as shown in FIG. 7(b). And such minute voids lead to a decrease in film density.
These minute voids (defects) present a new problem of deteriorating the resistance of the film to moisture absorption. In other words, introducing fluorine atoms into the film to lower its dielectric constant increases the minute defects due to three- or four-membered rings, thereby permitting the easy infiltration of moisture into the film from the atmosphere. The result is that the film changes into one which contains a large amount of moisture. Such a moisture-rich film has a dielectric constant as high as about 4.0. In addition, it causes imperfect contact at via holes due to gas (mainly water vapor) escaping from it in the subsequent process as shown in FIG. 8. (This is referred to as poisoned via failure.) FIG. 8 shows a structure which is composed of a silicon substrate 101, an aluminum interconnection 102, a fluorine-containing silicon oxide film 103 (of conventional type), a titanium nitride film 105, and a tungsten film 106. It is to be noted that voids are formed in the fluorine-containing silicon oxide film 103 and moisture 107 migrates from them to cause contact failure.